Automatic defrosting means for refrigeration apparatus



March 6, 1956 E. M. SORENG ET AL 2,737,025

AUTOMATIC DEFROSTING MEANS FOR REFRIGERATION APPARATUS Filed Oct. 8. 1952 TO MOTOR.-

COMPIZESSER UNIT TEMPERATURE 8L RESPONSIVE I SWITCH FOR momcomesssn UN \T /Z DOOR OPERATED v PUSH BUTTON SWITCH m J E )J A MA 39 40 1' [52 r /7 Q 3,

'wm Edy/:72." M Saran; [2" 1 1274 5 171 nite; rates AUTOMAT C. DEF ROSTIN G MEANS. FOR REFRIGERATION APPARATUS Edgar M. Soreng, Skokie, and Irving Gebel, Oak Park,

Ill., assignors, by mesne assignments, to Screng Eroducts Corporation, a corporation of Delaware Application October 8, 1952, Serial No. 313,708

6 Claims. (Cl. 6 23) This invention relates to refrigeration apparatus and has; more particular reference to the provision of automatic defrosting means for refrigerators.

In general it is the purpose of this invention to provide defrosting means which includes an electrical heating coil to effect heating of the evaporator unit of a refrigerator to a defrosting temperature, and a defroster switch for controlling the operativeness of the heating coil.

More specifically, it is a purpose of this invention to provide means for automatically actuating the defroster switch to its defrosting position as a consequence of opening of the refrigerator door a certain number of times, and for automatically resetting the defroster switch to terminate defrosting.

Accordingly, it is an object of this invention. to pro,- vide an electrical timing device which is energized by closure of a door actuated switch on they refrigerator each time the refrigerator door is opened, and which, when so energized a number of times, effects actuation of the defroster switch to initiate defrosting of the evaporator unitof the refrigerator. As a specific'example,

the timingdevice may comprise a solenoid motor and a movable actuating: member for the defroster switch, driven by the solenoid motor to be advanced thereby part way toward a switch tripping position each time the refrigerator dooris opened to effect energization of; the solenoid motor;

A further object of this invention resides in the pro-.- vision of automatic defrosting means of the character described; but wherein the electrical timing means will be rendered inoperative as a consequence of actuation of the defroster switch to its defrosting position and will remain inoperative throughout the entiredefrosting period.

Another object of; this invention resides in the pro.- vision of thermally. responsive resetting means: for the defroster switch. for moving thev same out of its, defrosting position, thereby terminating the defrosting cycle, as a'consequence ofattainment of a predetermined; dc.- frosting; temperature in the interior of the refrigerator;;

Still, another object of the invention resides in the'provision of automatic defrosting means of the character describedwith inst-rumentalities which periodically effect intermittent energization and de-energization of the electrical timing; device injthe event: the refrigerator door is left open for a protracted period of time during'normal operation of the refrigeration apparatus,

Withthe above, and other objects in View; whichwill appear as thedescript-ion proceeds, this invention resides in the novel; construction, combination and arrangement of; parts substantially as hereinafter described and more particularly defined by the appended claims, it being understoodthat such-changes in the precise embodiment of the; herein disclosed invention. may be made as. come within the scope of-the claims.

The accompanying. drawing illustrates one completeertample of the physical embodiment of the. invention constructed according to the best mode so far devised "for the practical application of the principles: thereof, and iri'whicli'tlie single figure isa combined mechanical and electrical diagram illustrating the manner in which defrosting of: the evaporator unit of a refrigeration apparatus is automatically controlled by the defrosting nieans of this invention.

Referring now more particularly to the" accompanying drawing; the. numeral 5 generally designates: the evaporator unit of a refrigeration apparatus (not shown): As is customary, cold refrigerant: is led into the: evaporator from. a: condenser (notshown); through a duct; 6, and after circulating: through the, evaporator unit the refrigerant discharges through. a duct Z for return tothe compressor (not shown);'of theapparatus'.

It is; to berunderstood of coursethat the refrigeration apparatu includes a temperature responsive switch unit indicated as; at; it. for; controlling: the; operation: of the motor-compressor unit (not, shown), and: the temperature responsive: switch unit may be of the fluid pressure; operated typ having a. temperature sensitive bulb 9 positioned' adjacent, to the evaporator unit and; communicating with the switch unit 8 through a duct10;

Therefrigeration apparatus also includes: the,- usualpush button switch, 12. normally heldi'n, an open position by the refrigerator doorwheneverthe dooris closed, the

'- switch being biased to a closed position which-itassumes whenever the refrigerator door is opened. Normally, the door operated push button switch; has the; sole function of effectingenergization of the interior'light 14 of the refrigerator Whenever its door is; opened. For this purpose the push button switch and theinterior light 1 4. are serially connected in a, conductor 15; joined across a. pair. of electrical supply lines L- l and L-Zz, As indicated/in. the. diagram, the supply line. L-1 may continue on to, the motor-compressor unit, while the; supply line L.2 is connectable with the. motor-compressor unit through the temperature responsive switch unit. 8 of the refrigerator.

The automatic defrosting, means. of this invention comprises a defroster switch 16, an electrical timingdevice indicated generally by the numeral 17 for eifectin actuiillOI'l: of the defroster switch'out of its position shown'in solidlines to a defrosting position indicated in constructionlines, and a heating coil 18. which is connected across thelihes"L.-1,. and. L-2. by the defroster switch- 16; when the latter is actuated to its defrosting position. The heating coil 18, of course, is positioned: to effect heating of the evaporator unitto a, defrosting temperature whenevellr the coil is-.energized at the initiation of the. defrosting Cy; Q.

The defroster switch 16 is preferably, although. not necessarily, of, the snap-acting over-center type, Since theconstruction. of. the switch 16 forms no part of, this invention and is generally well known, it will sufiice to note that the switch comprises a flexible. contact. cartying blade 20; of electrically conductivev material, having' one end anchored to. a stationary support. as at 21 and: having. a movable; contact 22. at its; free end remote from the support 21. The switch includes a'secondzflexibl'e blade, 23 likewise having one endanchored to. thesup'port 21v with its free end extending in the same general direction; as; the; contact bladebut terminating a distance short: Qfthe outer end ofthe latter, The shorter blade .23 is flatwise flexibl'e in oppositedirection's" toward and beyond the plane of the contact blade'20', audit is yieldingly held at either one side or the other of the contact blade by means of a compression sprin confined,

contactblade' 20' flexed to the "right andin a' position at 3 which the movable contact 22 as its outer end is in engagement with a stationary contact 25.

Consequently if a force is applied to the shorter blade 23 to move the same to the right toward and beyond the plane of the contact blade 20 the compression spring 24 effects snap actuation of the contact blade in the opposite direction to carry the movable contact 22 on its outer end into engagement with another stationary contact 26, as indicated in construction lines in the diagram. As stated previously, the defrosting switch is in its defrosting position when the contact blade 20 has been actuated to the left to occupy the position indicated in construction lines, and in which the contacts 22 and 26 are engaged with one another.

When actuated to its defrosting position, the switch 16 completes an energizing circuit through the heating coil 18 to initiate defrosting of the evaporator unit 5. For this purpose the heating coil 13 has one of its ends connected with the line L-1 by a conductor 28 while its other end is connected with the stationary contact 26 by a conductor 29. Since the fixed end of the contact blade 20 is connected directly with the line L-2 by a a conductor 30, the coil 18 will be energized whenever the switch contacts 22 and 26 are in engagement.

When tripped to its defrosting position, the contact blade 20 of the switch remains engaged with the contact 26 until an actuating force is applied to the shorter blade 23 of the switch to effect snap actuation of the contact blade in the opposite direction, to its position re-engaging the stationary contact 25.

The timing device 17 includes a movable member 32, an actuator 33 movable therewith to effect snap actuation of the defroster switch to its defrosting position, and electrically operated control means shown as an electromagnetic motor 34 to drive the movable member 32. While the motor 34 may be of any desired type, it may conveniently comprise a solenoid 35, an armature 36 movable in one direction in response to energization of the solenoid and in the opposite direction under the influence of a tension type biasing spring 37. As shown, the armature has a ratchet coupling with the movable member 32 to move the same a distance in one direction each time the armature responds to energization of the solenoid.

The movable member 32 preferably comprises a ratchet wheel rotatably mounted on a shaft 38 and having a series of equi-spaced teeth 39 on its periphery. The armature is provided with a pawl 40 on its outer end to operatively engage the ratchet teeth and impart counterclockwise rotation to the member 32 whenever the solenoid is energized.

As an example, the ratchet wheel may be provided with 60 teeth and the working stroke of the armature may be restricted to the extent necessary to effect indexing of the ratchet wheel one tooth space each time the solenoid is energized. The means for so restricting reciprocatory motion of the armature may take any desired form, as for instance the stop 42 usually carried by the solenoid frame (not shown) engageable by the inner end of the armature to limit its attraction stroke, and a stem 43 on the outer end of the armature engageable with the abutment 44 to which the tension spring 37 is attached.

From the description thus far it will be apparent that the ratchet wheel will be advanced one tooth space each time the armature responds to energization of the solenoid 35, and that energization of the solenoid 60 different times will cause the ratchet wheel 32 to be rotated through one complete revolution. With the position of the parts shown in the diagram, the ratchet wheel has nearly completed the one revolution thereof necessary to effect tripping of the defroster switch 16 by a flexible finger 46 carried by an arm 47 on the actuator 33.

The actuator 33 is shown as rotatably supported on the shaft 38, alongside the ratchet wheel, and it is oscillatable in opposite directions relative to the ratchet wheel between limits defined by a pair of pins 48 and 49 on the wheel projecting axially therefrom and between which the arm 47 on the actuator projects. The actuator is yieldingly held in its counterclockwise limit of rotation relative to the ratchet wheel and in engagement with the leading pin 48 by means of a tension spring 50 connected between the ratchet wheel and the arm 47 on the actuator. Consequently the actuator may be swung in a clockwise direction, counter to the travel of the ratchet wheel, against the bias of the spring 59.

The outer end of the flexible finger 46 on the actuator arm is arranged to contact a projection 51 on the shorter blade 23 of the defroster switch shortly before the ratchet Wheel has been rotated through one complete revolution. Upon such engagement and during subsequent rotation of the ratchet wheel to complete its cycle of rotation, the finger 46 flexes and the tension spring 50 yields while at the same time sufficient force is exerted on the shorter blade of the switch as to effect snap actuation thereof. As soon as the switch snaps over, the actuator is returned to its counterclockwise limit of rotation re-engaging the pin 48 and the flexible finger 46 straightens itself to occupy a position a slight distance beyond the original position of the projection 51 on the defroster switch blade 23.

Upon such snap actuation of the defroster switch, defrosting is initiated in the manner previously described, and as will now be discussed, the timing device 17 is rendered inoperative for the duration of the defrosting cycle.

Since the solenoid 35 of the electromagnetic motor is to be energized each time the door of the refrigerator is opened, during normal operation of the refrigerator, the solenoid is connected across the lines L-l and L-2 in parallel with the interior light 14 and in series with the door operated push button switch 12. Since it is a feature of this invention that the electrical timing device is rendered inoperative during defrosting, the energizing circuit for the solenoid also leads through the defroster switch 16. Thus, a conductor 53 connects one end of the solenoid with the conductor 15, between the door operated switch 12 and the interior light 14, while the other end of the solenoid is connected with the stationary contact 25 of the defroster switch by a conductor 54.

In this manner whenever the defroster switch is in its normal position, illustrated in solid lines in the diagram, the closure of the push button switch 12 as a consequence of opening of the door completes an energizing circuit through the solenoid 35 leading from line L-l through the switch 12, the solenoid 35, conductor 54, the contact blade 20 of the defroster switch, and the conductor 30 to line L-2; and the armature is moved to its attracted position defined by its engagement with the stop 42 to advance the ratchet wheel one tooth space in a counterclockwise direction. The ratchet wheel of course, will be advanced one tooth space, as described, each time the refrigerator door is opened, and after 60 such advances (one complete revolution) the defroster switch is tripped by the finger on the actuator 33 to initiate defrosting and to preclude any further rotation of the ratchet wheel should the refrigerator door be opened one or more times during defrosting. This has the advantage of assuring that the ratchet wheel will always have to be propelled through a complete revolution before the next defrosting cycle can be commenced.

Inasmuch as the defroster switch 16 remains in its defrosting position following tripping thereof by the timing device, it is necessary to provide means for resetting the defroster switch to terminate the defrosting cycle, and such means may conveniently comprise a temperature responsive fluid pressure operated device 56 of a well known type. This device comprises a bellows 57 enclosed in a fluid tight chamber or housing 58 containing a fluid, and a temperature sensitive bulb 59 positioned adjacent to the evaporator unit 5 and communicating with the interior of the housing 58 by a duct 60.

Du ng de ro ing he r seio. emperature-atthe oval!" orato u it a d. etected by t e M111 cau es i -i crease. i -flu d p s e n h bello hous ng. o'comp ss he bellows and force an actuating button 61 carried thereby outwardly of the housing and-against the shorter blade 23 of the defroster switch 16; By the time. the frosthas been eliminated from the evaporator unit, the-actuating button will have travelled farenough outwardly of the housing as to force the switch blade 23 beyond the plane ofthe longer blade 20 to thereby cause snap-action of the switch and resetting thereof to its normal position. With such resetting ofthe defroster switch, the circuit for the heating coil is broken and defrosting is terminated; and a new timing cycle eontrolledby opening of th refrigerator door may begin.

If, the heating. coil L8 is wound around or positioned closely adjacent to the supply duct 6 through which the cold refrigerant enters the evaporator unit from the condenser, defrosting may talte; place in a relatively short time provided that the motor-compressor unit is free to operate during the defrosting cycle. Forthis reason the energizing circuit for the motor-compressor unit of the refrigerator should not in anywise depend upon the position of the defroster switch. Hence, even though the circuitfor the motor-compressor unit may not be closed at the time the defroster switch is stripped to initiate defrosting, the motor-compressor unit-will begin to operate shortly, thereafter, as soon as the temperature responsive switch 8 closes in the ordinary Way,

Thereafter, though cold refrigerant is discharged from the condenser of the refrigerator toward theevaporator unit through the duct 6, the refrigerant will be heated by the coil 18 before it enters the evaporator unit, with the result that the temperature of the-evaporator'unit will be caused to rise substantially uniformly for the period of time it takes for frost to drop from or melt on its; exterior.

Since the timing device 17 is rendered operative as a consequence of opening of the refrigerator door and effects advance of the ratchet wheel 32 one tooth space each time the refrigerator door is opened, and would require closure of the refrigerator door before, the electromagnetic motor can again be operated to advance the ratchet wheel another tooth space the next time the refrigerator door is. opened, there would ordinarily be some danger that excessive amounts of frost would build up on the exterior of thc'evaporator unit in the event the refrigerator door was left open for long periods of time.

According to this invention, however, means are provided for effecting periodic energization and de-energization of the solenoid motor of the timing device if the refrigerator-door should be left open for any reason for a protracted interval, so as to assure under all conditions of use that defrosting Will be initiated each time a predetermined amount of frost is formed on the evaporator unit, or more precisely, whenever the refrigerator door has been open for a predetermined total time.

The means for automatically elfecting periodic energization and de-energization of the solenoid motor comprises a small heating coil 62 and a bi-metallic switch 63 positioned adjacent to the heating coil to be responsive to the heat thereof, and both connected in series circuit in the conductor 54 joining one end of the solenoid 35 with the stationary contact 25 of the defroster switch. Being connected in the conductor 54 in this manner it will be immediately apparent that the solenoid 35 can be energized only when the bi-metallic switch 63 is closed and the defroster switch is in its normal position shown.

By this arrangement some heating of the coil 62 will take place each time the refrigerator door is opened and the ratchet wheel is advanced one tooth space by the solenoid motor, but the bi-metallic element of the switch 63 is selected so as to be relatively uninfluenced by the heating coil 62 if the refrigerator door is left open or only a normal period of time, for instance. on the order of about- 10 seconds. If the refrigerator door is left open forlonger periods of time, the coil 62 heats to a greater extent and causes fiexure of the bi-meta-llic element of the switch 63 outof engagement with its-contact 64, to a position such as indicated in construction lines to break the energizing circuit for the solenoid 35 and the coil 62 for the period of time it takes for the bi-metallic element to cool and return to its, switch closing position.

Thus, for example, the characteristics of the bi-metallic element may be such that the energizing circuit for the solenoid 35 and the heating coil 62 will be disrupted for a period of approximatelyone. minute before the bimetallic switch is reclosed and the circuit for the solenoid motor re-established to effect advance of the ratchet wheel another tooth space.

Such opening and closing of the bi-metallic switch, of course, continues periodic-ally as long as the refrigerator door is left open so that the timing device, though it opcrates each time the door is opened, is not dependent alone upon the physical act of opening of the door, but in addition integrates the number of times the door has been opened for a normal period of time with the surpluses of time over normal which the door was allowed to remain open and effects initiation of defrosting accordingly.

From the foregoing description taken together with the accompanying drawing it will be readily apparent to those skilled in the art that this invention provides an unusually simple but highly reliable means for effecting automatic defrosting of a refrigeration apparatus; and that its chief advantages result from the use of a door operated switch in the control circuit for the electrically operated control or timing means so as to enable the control system to be mounted anywhere in the refrigerator cabinet remote, from the door opening. Other highly important advantages are that the, timing means integrates the number of times the door is opened for a normal period of time with the surpluses of time over normal which the door was allowed to remain open; and that the timing device is rendered inoperative throughout the entire defrosting period so that the periods of normal operation of the refrigerator will not be curtailed regardless of the number of times the door may have been opened during defrosting.

What we claim as our invention is:

1. Means for effecting periodic defrosting of the evaporator of a refrigerator comprising: a door operated switch arranged to close as a consequence of opening of the refrigerator door; defrosting means for the evaporator including a defroster switch movable from a first position-to a second position to initiate defrosting of the evaporator; a solenoid motor controlled jointly by said door operated and defroster switches to be energized only when the defroster switch is in said first position thereof, each time the door operated switch is closed, said solenoid motor including a movable member which is advanced a predetermined distance each time the solenoid motor is energized and which is operable upon motion throughout a predetermined range f travel to effect shifting of said defroster switch from the first to the second designated position thereof at which defrosting is initiated; and means in the energizing circuit of the solenoid and thus also governed by the door operated and defroster switches for effecting periodic energization and de-energization of the solenoid in the event the refrigerator door is left open for a protracted period of time.

2. The defrosting means set forth in claim 1 wherein said means for effecting periodic energization and deenergization of the solenoid comprises a normally closed thermally responsive switch and a heating element both connected in series with the solenoid so that in the event the refrigerator door is left open for a protracted period of time the temperature of the heating element will rise to a degree effecting opening of said thermally responsive switch to break the circuit through the solenoid and the heating element, whereby the thermally responsive switch will remain open for the period of time it takes the heating element to cool to the degree necessary to effect reclosure of the thermally responsive switch.

3. In an electric refrigerator of the type having an evaporator, electrically operated defrosting means for the evaporator, and a door: a door operated switch arranged to close as a consequence of opening of the refrigerator door; a two position defroster switch for the defrosting means movable from a defrosting position to a second circuit controlling position in which it is in series circuit with the door operated switch and renders the defrosting means inoperative; a member movable through a predetermined range of travel; electrically operated control means governed jointly by said door operated and defroster switches and connected with said movable member to move the same part way through its range of travel each time the door is opened as long as the defroster switch is in said second position thereof in series circuit with the door operated switch; and means operated by said movable member as a consequence of movement thereof through its predetermined range of travel for effecting shifting of said defroster switch from its second circuit controlling position to its defrosting position, so that said electrically operated control means is rendered inoperative whenever defrosting is taking place.

4. Means for effecting periodic defrosting of the evaporator of a refrigerator of the type having electrically operated defrosting means for the evaporator, and a door, comprising: a door operated switch arranged to close as a consequence of opening of the refrigerator door; a twoposition defroster switch for the defrosting means movable from a defrosting position to a second circuit controlling position in which it is in series circuit with the door operated switch and renders the defrosting means inoperative; a member movable through a predetermined range of travel between defrosting periods; electrically operated control means connected with said movable member to impart movement thereto; an energizing circuit for said electrically operated control means completed through said door operated switch and the defroster switch only when the latter is in said second circuit controlling position thereof in series circuit with the door operated switch, whereby said electrically operated control means is operated and said movable member is moved thereby each time the door is opened except when the defroster switch is in its defrosting position; means on said movable member for effecting shifting of the defroster switch from its second circuit controlling position to its defrosting position upon motion of the movable member through its predetermined range of travel; and thermally responsive 8 resetting means operable upon attainment of a predetermined defrosting temperature in the interior of the refrigerator for effecting return of the defroster switch to its second circuit controlling position to thereby terminate defrosting.

5. The defrosting means set forth in claim 4 wherein said electrically operated control means comprises a solenaid governed jointly by the door operated and defroster switches, and an armature biased in one direction but movable a predetermined distance in the opposite direction in response to energization of the solenoid; and wherein said movable member is rotatable and has a ratchet coupling with the armature to be indexed thereby a predetermined distance representing a fraction of said predetermined range of travel of said member each time the solenoid is energized.

6. In a refrigerator having a door and an evaporator, defrosting means comprising: a normally open switch arranged to close as a consequence of opening of said door; an electrical heating element for heating the evaporator to a defrosting temperature; a defroster switch movable from a first position to a second position to complete an energizing circuit for said heating element; an actuator for said defroster switch recurrently movable to a predetermined position at which the actuator effects shifting of the defroster switch to its second position to initiate defrosting; electrically operated means for advancing said actuator part way toward said predetermined position thereof each time the refrigerator door is opened, said electrically operated means including a solenoid energized by closure of said door operated switch only when the defroster switch is in said first position thereof, whereby defrosting may be initiated after the refrigerator door has been opened a number of times; and electrically operated means governed by the door operated and defroster switches for effecting periodic deenergization of said solenoid in the event the refrigerator door is left open for a protracted period of time during normal operation of the refrigerator.

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